Physiological and morphological properties of identified basket cells in the cat's visual cortex.

In 87 cells studied physiologically, and filled intracellularly with horseradish peroxidase (HRP), we have found four cells which make multiple contacts with the perikarya of their post-synaptic targets. These cells are all multipolar non-pyramidal neurones with elongated smooth dendrites. Three resemble the classical "basket cells" of Ramón y Cajal (1911), having widely distributed axons which contribute to the "nids pericellulaires" around pyramidal cell perikarya. The fourth cell has a much more restricted axon virtually confined to layer 4 and appears to contact principally small, probably non-pyramidal, cells. Two of the basket cell axons have been examined by electron microscopy and make symmetrical, Gray's type II contacts with the perikarya and apical and basal dendrites of pyramidal cells. Ten percent of the synapses are on dendrites of non-pyramidal cells. The axon arborizations of all four cells are distributed in a patchy fashion. In two cells examined for the purpose, very few boutons were found within 100 micron of the cell body and a radially aligned cylinder of the same diameter extending from the cell body to the pial surface. The physiological properties of these structurally similar cells are far from uniform. They can be activated mono- or polysynaptically, by X- or Y-type lateral geniculate input, and can have S or C type receptive fields. Two were activated, probably monosynaptically, via callosal afferents. These cells may play an important role in the inhibitory mechanisms of the cortex.